The present invention relates to a method of co-forming an article from a metal foam and a powdered metal component. The present invention also relates to the co-formed metal foam article formed by the method thereof. The article of the present invention is suitable for a number of purposes including enhancing heat and mass transfer and promoting chemical reactions.
There are a number of known methods for forming a metal article from a metal foam and a metal component. However, in these known methods, the metal component has already been formed and solidified by a conventional metal-forming method such as extrusion, rolling, forging and casting, prior to being contacted with or joined with the metal foam. For example, in some known methods a cylinder of polymeric foam that has been impregnated with a slurry coating of powdered metal is inserted into a solid metal component such as a tube. This coated polymeric foam unit is referred to as a xe2x80x9cgreenxe2x80x9d assembly. The green assembly is then placed into a sintering furnace and heat-treated to volatize the polymeric foam and to sinter the metal foam. The metal foam is then contacted with or joined to the metal component(s) by a conventional bonding method such as brazing, welding, soldering, and crimping. Examples of these known methods wherein the metal component has already been formed and solidified by a conventional metal-forming method prior to being contacted with or joined with the metal foam are set forth below.
U.S. Pat. No. 5,943,543 relates to a heat transmitting member which is capable of improving heat transfer efficiency wherein the member is comprised of either a metal pipe or a metal plate.
Japanese patent application JP 60050395 discloses a method of forming a radiator wherein pipes are wrapped with a metal foam.
U.S. Pat. No. 5,943,543 discloses preparing a cellular synthetic resin structure such as a polyurethane foam which may be coated with an adhesive. A metal powder is then deposited onto the cellular structure. The metal pipe or metal plate which has already been manufactured by a conventional metal-forming method is placed adjacent to one or more surfaces of the polyurethane foam such that the foam and the metal pipe or metal plate are placed in contact with the polyurethane foam. Thereafter, the polyurethane foam is burnt away by heating the polyurethane foam and the metal pipe or metal plate to an appropriate temperature such that the metal material is fixed on and made unitary with one or more surfaces of the metal pipe or metal plate.
U.S. Pat. No. 6,085,965 discloses a method of forming low density core metal parts by pressure bonding face sheets already manufactured by conventional metal-forming methods to a porous foam metal core and simultaneously densifying the core. The method includes the steps of providing a porous, foam metal core and simultaneously pressure bonding first and second solid metal face sheets directly to opposite sides of the core and densifying the core by applying heat and uniaxial forge pressure to the first and second face sheets and to the core for a predetermined period of time.
However, there is a very significant problem that results from these known methods. Shrinkage occurs in the foam whereas little or no shrinkage occurs in the metal component such as the metal plate or metal tube, thereby creating a gap or space between the metal foam and the metal plate or metal tube. This gap creates numerous problems including, for example, a reduction in heat transfer efficiency. Thus, until now, there has been a need for a method of forming an article from a metal foam that overcomes the problems resulting from shrinkage. The method of the present invention surprisingly solves this problem.
The present invention relates to a method of making an article that is comprised of a metal foam joined to a metal component. In particular, the present invention relates to a method of co-forming a powdered metal component and a coated polymeric foam to form a metal article. In the method, a powdered metal component is formed from a powdered metal composition. In the method, a polymeric foam is also coated with a powdered metal composition which may be the same or different than the composition of the powdered metal component. The coated polymeric foam is placed in contact with the powdered metal component to form a composite, and the composite is heat-treated. The heat-treatment volatilizes the polymeric foam and solidifies the powdered metal component and the coating such that the co-formed metal article is formed. An advantage of the method of the present invention is that it eliminates any gaps or spaces associated with shrinkage of the metal foam by allowing the powdered metal component to shrink along with the metal foam. As a result, a good, continuous bond is created between the metal foam and the powdered metal component.